1. Technical Field
The present invention relates to a low power consumption technology in a processor having a low power consumption operation mode, and in an information processing device having the processor incorporated therein.
2. Related Art
In late years, in the field of an electronic information device and a portable information processing device, in addition to improvement of a processing ability of a processor to be used for these devices, it is important to reduce an power consumption of the processor, particularly, in a technical field of a portable information processing device.
Reduction of the power consumption is generally achieved by controlling a frequency of a clock supplied to the processor, and controlling supply of a power supply voltage (for example, refer to a patent document 1: JP-A-2001-517332 and a patent document 2: JP-A-2002-543513). As a driving mode of a conventional processor, a low power operation mode is provided, and an power consumption of the processor is made lower than that of a normal operation mode (i.e., a non-low power operation mode) so as to lower the power consumption of processor alone. In other words, in the conventional low power consumption mode, a clock frequency and a power supply voltage to be supplied to the processor is controlled so that the power consumption of one processor, namely, a calorific value of the processor is made small.
As described above, the conventional low power consumption mode focuses attention on the power consumption per unit time of the processor. However, from a view point of a battery drain, electric energy to be consumed in total in terms of time should be considered. That is, the amount of power consumed to complete a predetermined amount of process should be considered, and in this case, the conventional low power consumption mode does not always realize the low power consumption operation.
In the case of driving a processor in the conventional power consumption mode, it is true that the power consumption per unit time in the processor is reduced. However, in this case, since the power supply efficiency is decreased and the processing ability of the processor is lowered, it takes a longer time to complete a predetermined amount of process, and an expended time of the battery is increased. Therefore, even if the power per unit time is reduced, it takes a longer time to complete one process, and this does not consistently results in that the power consumption in its entirety (i.e., the power consumption per time×time for processing) is reduced. In other words, if a ratio of increase of the processing time by the low power consumption mode exceeds a ratio of decrease in the power consumption in the low power consumption mode, from a view point of the battery consumption, this results in increase in the power consumption in its entirety.